I have received some good advice on this forum about combustion cannons. I want to make one capable of handling pure oxy/acetylene fuel mixtures. Do people already do this? If so, what material do they use? I want to make a powerful combustion spudder that has all the goodies, like chamber fan (replaceable) full length spark strip or equivalent ( 3-4 spark gaps) and adequate ventilation fan. I would also like breach loading since jamming a tennis ball down a 3-4 ft barrel can be a pain. Anyway..on to my main question. I want to make a simple combustion spudder out of aluminum with these features. HOW THICK should it be? I was thinking 1/4" wall thickness, not only so it won't explode, but so that it won't easily dent if dropped or banged. Aluminum is kind of soft after all, but relatively cheap to machine/weld. I don't have much money to spend on this or else i'd just draw something up and have it made and consider revisions later. Oxy/Acetylene capable thickness with aluminum...how thick? Do I need aluminum? Maybe SCH80 PVC? I dunno.

If it's your first, don't do it. If you are experienced, don't do it. If you're Larda.... Go right ahead. But in all honesty, pursuing acetylene may be a form of suicide. Acetylene does not burn, it explodes. In poorly designed hybrid guns, their controlled burns sometimes turn into explosions, a phenomenon called DDT (deflagration to detonation transition). DDT usually spells the death of the cannon. If you fired a simple combustion using acetylene, you would be experiencing the effects of DDT (while not DDT itself) on every shot. There are very few people who have the resources to build cannons suitable to take that kind of punishment.

I plan on making a low (2-3) mix hybrid out of aluminum tube with a 4" diameter. The walls are 1/16" thick. With a 3x air/propane mix the highest theoretical pressure (according to HGDT) is 333.3 psi which gives me a safety margin of about 4 using Barlow's formula to calculate the tubes theoretical burst pressure.

In reality though, with the burst disks I'll be using the pressure won't exceed 200 psi at most and usually alot less than that.

If I were you though, I'd just buy the thickest aluminum tube you can afford. Check eBay, that's where I found mine.

the reason I was thinking acetylene was because I wanted something with excellent power, yet simple to use. From what i'm seeing it sounds like acetylene is just nto a good fuel to use in any case really. Sounds like for more power i'll just have to make a well optimised advanced combustion. Maybe the simple addition of pure oxygen alogn with the propane would significantly increase power.

Moonbogg wrote:Maybe the simple addition of pure oxygen alogn with the propane would significantly increase power.

Be very careful doing that as well...it will certainly work..duhh... Considering the danger and until you have some more experience under your belt, there's really no reason to use O2 in a 1X spud gun. Good ole air has plenty in it and the nitrogen acts as an inert buffer gas during the burning helping to prevent DDT. A pure propane/MAPP and O2 chamber is a potential DDT bomb just waiting to go off.